A valve actuating mechanism used in an internal combustion engine is influenced by wear or thermal expansions, whereby a space or a clearance formed at the valve is deformed during operations and adversely affects the output and results in an undesirable noise. An oil pressure lash adjuster has been therefore used to rectify the deformed space or clearance.
A directly actuating valve mechanism has been designed to be light in weight for a cam to directly strike an end of a valve shaft this mechanism has been also employed with the oil pressure, lash adjuster as shown in FIG. 7.
The oil pressure lash adjuster includes a housing and an oil pressure unit Y of the lash adjuster located therewithin, and is placed between a cam 300 and the end of a shaft 400.
The oil pressure unit Y is slidably mounted on the outer circumference of a plunger 101 shaped as a cylinder having an oil orifice 104 in its bottom. The unity Y comprises a cylinder-shaped body 100 of defining a high pressure chamber 102 at with the bottom of the body 100; an elastic member 105 provided in the high pressure chamber 102 and biasing the body 100 downward; a check valve 106 disposed in the high pressure chamber for opening and closing the oil orifice 104; and a valve spring 107 supporting the check valve 106 and a check valve cage 108 in the high pressure chamber 102.
The oil pressure unit Y is located in the housing X, defining a main reservoir 103 as an oil storage between the rear surface of a face disc 202 and the hollow portion of the plunger 101 as well as a sub-reservoir 200 communicating, via an overflow recess 203, with the main reservoir 103 partitioned with the circumferential wall of the plunger 101, the sub-reservoir 200 being supplied with the actuating oil through an oil feed orifice 500 of a cylinder head and an oil orifice 510 of the housing X.
On the other hand, a cam 300 contacts the face disc 202 of the housing X, while the end of the valve shaft 400 contacts the closed face of the body 100, so that the cam 300 strikes the end of the valve shaft 400 via the oil pressure lash adjuster.
The oil pressure lash adjuster makes use of a incompressibility of the actuating oil when applying pressure to the actuating oil filling in the high pressure chamber 102, and an expansion property of the elastic member 105 which expands in the chamber when releasing the pressure so as to bring the space to be zero which space has been thermally deformed in the valve actuating mechanism.
A part of the oil to be supplied to the sub-reservoir 200 leaks via a space between the outer circumference of the oil pressure unit Y (the outer circumference of the body 100 in the drawing) and the sleeve 201 forming a partition of the sub-reservoir 200.
When the internal combustion engine stops while a cam nose 301 keeps pressing the face disc 202 of the housing X, the oil pressure unit Y is compressed as shown in FIG. 8, that is, it is in its most shortened (bottom condition). If the engine restarts under this condition, the sliding stroke between the plunger 101 and the body 100 is maximum, and the oil is most absorbed into the high pressure chamber 102. But if the oil leaks as mentioned above when the engine stops, the oil is not supplied thereinto from a cylinder head, and accordingly the oil is not supplied enough into the main reservoir 103 from the sub-reservoir 200. Therefore, when restarting the internal combustion engine, an air is absorbed together with the actuating oil, into the high pressure chamber 102 and the incompressibility of the actuating oil in the chamber 102 when the plunger 101 is pressed, is considerably lost (the incompressibility becomes soft and called as "sponge" condition) so that the space of the valve cannot be rectified.